A performance of an internal combustion engine having a magneto for a work machine such as a chain saw, a grass mover, and the like depends on how combustion is achieved under environmental conditions.
Accordingly, to achieve an output of a predetermined level, better fuel consumption, and reduction of exhausted substances, it is preferable to derive a particular engine performance by adjusting, for example, an air/fuel ratio to a value apart from a theoretical air/fuel ratio. Further, when it is possible to find ignition timing at a rotation angle of a crank before a piston reaches an upper dead point of a compression stroke, ordinary users can carry out maintenance for reducing the fuel consumption and the exhausted substances and enhancing the engine output.